Chemically induced changes in the geotechnical response of cementing paste backfill in shaking table test

Cemented paste backfill(CPB) is extensively used for underground mine support and/or tailings management.However,CPB behavior under cyclic loadings might be affected by the chemistry of its porewater,which often contains sulphate ions.Till today,no studies have addressed the effect of sulphate on the response of CPB to cyclic loadings by using shaking table technique.This study presents new findings of assessing the effect of the sulphate in the pore water of CPB on its geotechnical response to cyclic loading by using shaking table.CPB mixtures were prepared(with and without sulphate),poured into a flexible laminar shear box,cured to 4 h,and then exposed to cyclic loading using one-dimensional(1D) shaking table.Several parameters(e.g.pore water pressure,settlement,lateral deformation,acceleration,electrical conductivity,effective stress,and liquefaction susceptibility) were monitored or determined before,during,and after shaking.Obtained results indicate that the sulphate-bearing CPB cured to 4 h can be prone to liquefaction under the studied conditions.However,sulphate-free CPB samples are resistant to liquefaction.These results are expected to contribute to a better understanding of the effect of water chemistry on the cyclic behavior of CPB,consequently enhancing the cost-effective design of CPB structures.     

The effects of heat treatment on some technological properties in Uludağ fir (Abies bornmuellerinana Mattf.) wood

Heat treatment is often applied to improve the dimensional stability of woods. In this study, the effect of heat treatment on some mechanical properties of Uluda? fir wood (Abies bornmuellerinana Mattf.) having industrially high usage potential and large plantations in Turkey was evaluated. Samples collected from Bolu Forest Enterprises, Turkey were subjected to heat treatment for varying temperatures and durations. Then, the treated and control samples were tested for some mechanical properties; compression strength, bending strength, modulus of elasticity in bending, janka-hardness, impact bending strength and tension strength perpendicular to grain. The results indicated that treated samples had lower mechanical properties compared to the control samples. In addition, increase in temperature and durations decreased the mechanical properties.     

Mechanical behaviour of a compacted well-graded granular material with and without cement

Cement additions improve the performance of granular soils. However, most literature examples of cement additions are in poorly graded sands, either to mimic the behaviour of sandstones or to accentuate the mechanical differences between cemented and uncemented soils. In this article, the behaviour of a well graded granular soil, used for base and sub-base of roads, was studied by doing triaxial tests on cemented and uncemented samples. Samples were compacted to achieve a dense fabric and tested at stresses commonly used in practice. Sieving was used to understand if breakage is important and to determine the grain size distributions of the samples after compaction and shearing. The results show that the addition of small percentages of cement greatly increase stiffness and dilation. Thereby, generating larger strengths; this is particularly important at low confining stresses in roads and parking areas, where this material is commonly used. At large strains, the results show that different Critical State Lines exist for both the uncemented and cemented soils. Each line has a different slope, which is believed to be the result of the evolution of the grain size distribution of the cemented soil. The normalised data indicate that a unique state boundary surface can be determined for all three tested soils.     

Numerical investigation of the heat transfer in an aeronautical composite material under fire stress

The use of composite materials for aeronautical applications has been growing since several years because of the opportunity to produce lightweight structures reducing the fuel bills and emissions. The need for fireproof certification imposes costly and time consuming experiments that might be replaced or complemented in the years to come by numerical calculations. The present work creates a CFD numerical model of a fireproof test. As an example, a composite part located in an aircraft APU (auxiliary power unit) which provides electric power to the aircraft is investigated. A numerical calibration of the flame is conducted according to the fireproof standards. After that, a comparison between three different turbulence models shows that the k–ε realisable turbulence model is the more suitable for fireproof numerical tests with discrepancies lower than 16% between computed values and measured ones. The influence of an internal air jet is observed for velocities from 1 to 10 m/s. The results demonstrate a good evaluation on how this could reduce the wall temperatures and ensure the requirements of the certification rules compare to the actual external thermal protection used to ensure the certification requirements. Indeed, final temperature reductions up to 45% are found at reference point on the structure with the highest value of air jet velocity.     

Thermal and structural response of two-storey two-bay composite steel frames under furnace loading

The collapse of the World Trade Center Towers and other recent fires in tall buildings has motivated this study to understand the performance of structural frames under fire loading. Three two-storey, two-bay composite steel frames were constructed and subjected to dead loads by applying weight blocks, and to thermal load by placing the frame in a furnace. The furnace was specially designed to allow for controlled heating of the structural elements that formed the four compartments of the test frame. This paper describes the experimental results of furnace test conducted on the three full-scale composite frames. The three tests differed from each other in the number and location of compartments that were heated by the furnace. For each test, the structural elements were subjected to a heating-up phase followed by a cooling-down phase. The furnace temperatures and the steel and concrete temperatures recorded during the test are presented. The thermally induced horizontal displacements of the columns and vertical deflections of the composite beams are discussed. Observations on local buckling of the steel beam, cracking of the concrete slab and failure of the beam-to-column connections are tabulated. Experimental results of the three tests are compared with each other by studying the complete deformation process of the test frames over time. Results indicate that the deformation process of the test frames was highly dependent on the number and location of compartments that were subjected to thermal loading.     

复合墙体室内温度响应研究

针对建筑物内人体的热舒适性与内墙壁面温度的相关性,建立了具有复合材料墙体的房间内温度响应的数学模型.结果显示,在相同的加热(制冷)条件下,由相同材质、相同尺寸组合构成的复合材料墙体,在不同的材料排列方式情况下,室内的温度响应有很大的不同,这对间歇性供热(冷)房间内人体的热舒适性有较大的影响.     

Mechanical properties of microcrystalline branching selenite gypsum samples and influence of constituting factors

The high sedimentological variability of gypsum rocks has the effect that a univocal characterization of this material is not easy to establish. This is particularly true from the geomechanical point of view: when the mechanical properties of gypsum rocks are requested, it is therefore necessary to undertake detailed characterization analyses. Common facies of gypsum was observed in the Upper Miocene evaporitic succession (Messinian Salinity Crisis) within the whole Mediterranean Basin. In this work, mechanical tests were conducted on a site-specific facies, represented by the microcrystalline branching selenite. The tested samples came from the Monferrato area (northwestern Italy). Uniaxial compressive strength (UCS) tests were performed in order to obtain reference mechanical parameters. More rapid and economic point load test (PLT) and ultrasonic pulse velocity (UPV) measurements were additionally performed to verify their applicability as complementary/alternative methods for site characterization. Rock-type specific PLT-UCS and UPV-UCS relationships were established. A wide dispersion of the mechanical parameters was observed due to the heterogeneities of the studied material. Consequently, compositional, textural and microstructural observations on selected samples were performed. Two main material classes were recognized based on average grain size and total gypsum content, underlining the significant influence of the grain sorting on the measured mechanical properties.     

Engineering behavior of the Lisan Marl as a dyke foundation material: Dead Sea,Jordan

Problems have occurred with dykes constructed on the Lisan Marl to retain brine pumped from the Dead Sea, which is chemically processed to produce potash. In this study the engineering behavior, collapse potential and compressibility of the Lisan Marl were assessed by undertaking laboratory tests with both natural, distilled water and brine as the media. The results showed that the liquid limit and fine particles increased when the soil was mixed with fresh/distilled water compared with brine water. The soil can be classified as highly compressible with a low undrained shear strength. In terms of collapsibility, the soil could be classified as slightly collapsible upon inundation with distilled water and moderately collapsible when soaked in Dead Sea brine. The results are important when determining the height and nature of the dykes.      

Mechanical tests on a new non-cementitious grout, silica sol: A laboratory study of the material characteristics

This introductory study on mechanical properties aims to characterize silica sol and to improve knowledge of the suitability of silica sol as grout. Silica sol is a non-cementitious grout that consists of spherical particles of amorphous silica, with a diameter of 5–100 nm. For a testing period of six months, specimens of silica sol were kept at 8 °C with three relative humidities: 75%, 95% and 100%. During the test period measurements of the drying shrinkage, compressive strength, modulus of elasticity (Young’s modulus), shear strength and flexural strength were made. The results show that the strength of silica sol continues to increase for a long time and during the test period of six months the strength kept increasing. The increase of strength depends on the humidity to which silica sol is exposed but the humidity also affects the drying shrinkage. A lower humidity results in a faster increase in strength but also a larger shrinkage.     

A numerical investigation into the response of free end tubular composite poles subjected to axial and lateral loads

This paper presents a numerical investigation of cantilevered glass fiber-reinforced polymer (GFRP) tubular poles subjected to lateral and axial loads. A 3D finite element analysis was conducted to establish the lateral load–deflection responses under different axial loads and the axial load–bending moment interaction curves at ultimate. The model accounts for geometric nonlinearities and the composite laminate structure. Failure modes were established based on either material failure according to the Tsai-Wu failure criterion, or stability failure. The model was validated by using experimental results. A parametric study was then carried out on poles with various angle-ply and cross-ply laminates as well as different diameter-to-thickness (D/t) and length-to-diameter (L/D) ratios. The study showed that the reduction in axial strength as (L/D) ratio increases becomes more severe as (D/t) ratio is reduced. The GFRP laminate structure has a considerable effect on axial and flexural strengths of the poles for certain (D/t) ratios. It was also shown that axial load–moment interaction curves are generally linear. Increasing the fraction of longitudinal fibers in cross-ply laminates or reducing the fiber angle with the longitudinal direction in angle-ply laminates results in a larger interaction curve. A simplified design approach for the poles has been proposed.     

金属矿充填开采岩体移动对竖井围岩的变形破坏

采用数值模拟和地质力学分析的方法,对甘肃金川二矿区地下开采条件下, ^# 14 行风井变形破坏问题进行了研究,研究结果表明： ^# 14 行风井位于地下开采引起的岩体移动盆地的拉张区,受岩体移动变形影响剧烈,地下开采已经成为了影响竖井安全稳定的主要因素;无论是富矿开采还是贫矿富矿联合开采,竖井井壁的位移和应力分布规律大体相同,其大小与分布特征受断层影响突出,断层所在的部位仍然是竖井井壁的脆弱部位;地下开采引起的 ^# 14 行风井的破坏是以穿过井筒的断层出现活化为触发因素,以井壁发生错动、破裂、冒落为主要形式的断层效应的集中体现,这也将成为现阶段生产条件下竖井可能再次发生变形、破坏的模式。     

Thermal and structural behaviour of a full-scale composite building subject to a severe compartment fire

This paper presents a numerical investigation of the thermal and structural results from a compartment fire test, conducted in January 2003 on the full-scale multi-storey composite building constructed at Cardington, United Kingdom, in 1994 for an original series of six tests during 1995–1996. The fire compartment's overall dimensions were 11 m×7 m with one edge at the building's perimeter, using largely unprotected steel downstand beams, and including within the compartment four steel columns protected with cementitious spray. The compartment was subjected to a natural fire of fire load 40 kg/m² of timber, in common with the original test series, but the composite slab forming its ceiling was subjected to a uniform applied load of 3.19 kN/m², which is higher than the original.     

一种机械液压复合传动装置在扫路车中的应用

论述配置于单发动机专用车辆上的机械、液压复合传动装置,可实现车辆行车作业状态下的机械、液压复合传动,以及在车辆行车状态下的机械传动,油耗明显降低。     

Mechanical response of a partially restrained column exposed to localised fires

Recent trends in structural fire engineering research have focussed on the response of buildings with large open plan spaces to so-called travelling fires. These fires travel horizontally across the floor plate of a building and result in time and spatially varying thermal exposure and response of the structure to the fire. What has received little attention, however, is the effect that non-uniform thermal exposure has on columns. Recent tests conducted at SP demonstrated the effect of a small non-uniformity of thermal exposure, resulting in a thermal gradient of around 1 °C/mm, on a column exposed to a pool fire. The curvature resulting from a non-uniform thermal exposure where the column is pinned, or in cases where the column is partially restrained, will result in an eccentricity in the column’s loading and large second order effects.This paper describes the effect of thermal exposure varying in both the horizontal and vertical axes to columns by means of including this thermal boundary in a solution of classical Euler beam theory. The resulting solution allows for a variation in the stiffness of the rotational restraint at both ends of the column and a non-uniform temperature exposure through the column’s section and along its height. The resulting equations help to understand better the impact of the assumptions of ‘lumped capacitance’ on steel columns, suggesting a challenge to this assumption in some instances, as well as to enhance understanding of the impact of non-uniform fires on steel columns.     

锤击荷载作用下大直径钢管群桩的动力特性分析

上海某机械厂有一大直径钢管桩,用于所生产柴油打桩锤出厂前的试用。目前试桩已不满足新生产大吨位柴油打桩锤的试打要求,因此拟增加8根短桩与试桩组成群桩。由于锤击荷载作用下长短组合群桩中荷载的分配及沉降的研究较少,为得到合理的群桩加固型式,采用有限元方法研究锤击荷载作用下群桩的动力承载特性。首先建立单桩有限元模型,分析竖向静荷载作用下钢管桩的沉降,并将模拟结果与现场静荷载试验结果进行对比,验证有限元模型的准确性,再分析锤击荷载作用下单桩的动力响应;其次建立锤击荷载作用下的长短组合群桩有限元模型,分析承台质量、承台埋深、辅桩桩长对群桩桩顶荷载分布及沉降的影响。结果表明锤击荷载作用过程中,角桩、边桩桩顶最大压应力较大,主桩桩顶最大压应力较小;承台埋深越浅,群桩桩顶应力越大,沉降反而越小;承台质量、辅桩桩长对群桩动力特性影响不大。     

Dynamic response of a double-lined shield tunnel to train impact loads

A three-dimensional numerical finite element model was established by Abaqus to study the time-history curves of train-to-tunnel impact forces for impacts at different velocities, train configurations and oblique-impact angles. A concrete plastic-damage model was used to study the dynamic responses of a double-lined shield tunnel to train impacts by the HHT time-integration scheme. Model simulations showed that the impact force was related to the velocity and angle of the train at impact, as well as the train configuration. Two categories of characteristic force vs. time curve were found for the train-to-tunnel impact, and multi-peak Gaussian fitting was used to interpret the first category. The dynamic response increases with greater impact velocity and impact angle, while it greatly reduces when the thickness of the secondary lining is increased. Most of the tensile damage was seen ahead of the impact point (in the direction of travel), and compressive damage was concentrated behind, above and below the impact point. The average maximum tensile damage was found to exceed the compressive damage.     

Bacterial response to a shock load of nanosilver in an activated sludge treatment system

The growing release of nanosilver into sewage systems has increased the concerns on the potential adverse impacts of silver nanoparticles (AgNPs) in wastewater treatment plants. The inhibitory effects of nanosilver on wastewater treatment and the response of activated sludge bacteria to the shock loading of AgNPs were evaluated in a Modified Ludzack-Ettinger (MLE) activated sludge treatment system. Before shock-loading experiments, batch extant respirometric assays determined that at 1 mg/L of total Ag, nitrification inhibitions by AgNPs (average size = 1-29 nm) and Ag⁺ ions were 41.4% and 13.5%, respectively, indicating that nanosilver was more toxic to nitrifying bacteria in activated sludge than silver ions. After a 12-h period of nanosilver shock loading to reach a final peak silver concentration of 0.75 mg/L in the MLE system, the total silver concentration in the mixed liquor decreased exponentially. A continuous flow-through model predicted that the silver in the activated sludge system would be washed out 25 days after the shock loading. Meanwhile, a prolonged period of nitrification inhibition (>1 month, the highest degree of inhibition = 46.5%) and increase of ammonia/nitrite concentration in wastewater effluent were observed. However, nanosilver exposure did not affect the growth of heterotrophs responsible for organic matter removal. Microbial community structure analysis indicated that the ammonium-oxidizing bacteria and nitrite-oxidizing bacteria, Nitrospira, had experienced population decrease while Nitrobacter was washed out after the shock loading.     

大直径管桩在瞬态集中荷载作用下的 振动响应时域解析解

大直径管桩在低应变检测中应力波的传播是一个三维波动问题。将桩周土、桩芯土和桩底土对桩的作用简化为文克尔弹簧,将激振力用半正弦脉冲模拟,建立了大直径管桩在瞬态集中荷载作用下的振动响应计算模型,采用分离变量法和常数变易法求得了波动方程的时域解表达式。将该时域解与采用数值傅立叶逆变换计算得到的时域响应进行了对比验证,进一步将时域解析解计算结果与试验值进行了对比,验证了其合理性。采用得到的时域解计算分析了桩顶速度时域响应特性,结果表明：入射波到达时间和结束时间与波的传播距离成正比,从0°点到180°点基本呈线性变化;激振点的入射波结束时间等于输入脉冲宽度,其余测点的入射波结束时间与入射波到达时间的差值与输入脉冲宽度相等;入射波峰值对应的时间在激振点最小,从0°点到135°点逐渐增大,在135°点到180°点之间基本保持不变。     

内源爆炸荷载作用下无限弹性土体中圆柱形衬砌隧道的瞬态响应解答

内源爆炸荷载产生的振动响应对地下衬砌隧洞的安全非常重要。采用Fourier变换和Laplace变换,推导出内源爆炸荷载作用下无限弹性空间中圆柱形衬砌孔洞的瞬态动力响应无量纲解答,利用Fourier和Laplace逆变换数值方法,计算分析内爆炸荷载产生的振动在衬砌和周围弹性介质中的分布和传播衰减规律。计算结果表明,爆源中心处衬砌内表面径向位移、切向应力和衬砌外表面土体径向位移、切向应力最大,向左右两侧迅速衰减,在6倍衬砌内径处衰减为0;衬砌内表面径向位移、切向应力和衬砌外表面土体径向位移、切向应力时程曲线峰值爆源中心处最大,离爆源中心越远,峰值越小,且在t~*=10时衰减为0。     

The development of a finned phase change material (PCM) storage system to take advantage of off-peak electricity tariff for improvement in cost of heat pump operation

An experimental system consisting a longitudinally finned RT58 phase change material (PCM) in a horizontal cylinder has been conducted to evaluate the heat transfer characteristics of RT58. The investigation forms part of a wider study to investigate a suitable PCM to take advantage of off-peak electricity tariff. The system consisted of a 1.2 m long copper cylinder filled with 93 kg of RT58 with an embedded finned tube at the centre to serve as a heat transfer tube. The experimental data has been reported using hourly temperature profiles, isotherm plots, overall heat transfer coefficients and energy stored. The results show a quadratic relationship between heat transfer coefficient and the inlet HTF temperature within temperature range (62-77 °C) investigated. Increasing charge inlet heat transfer fluid temperature by 21.9% increased heat transfer coefficient by 45.3% during charging and 16.6% during discharge. The potential implication of integrating PCM storage system to an air source heat pump to meet 100% residential heating energy load for common buildings in UK has demonstrated that with an improvement in heat transfer, store size can be reduced by up to 30%.